Master Cylinder Swap with BAS - PeachParts Mercedes-Benz Forum

Roncallo · #1 10-21-2009, 08:36 PM

A lot of brake rotor and caliper talk on this forum. How about a master cylinder question. A master cylinder with wires???

My M120 560SL has front break calipers and rotors from an SL600 which is causing a significant bias problem (rear locks up early). I would also like to put the SL600 master on but I don't understand what the BAS motor on the side of this master does and what happens if I leave it disconnected. The current 560SL master has a 1"/0.75" bore front/rear and the SL600 has a 1.0625"/1". changing this master will increase the area ratio between rear and front from 0.56 to 0.88 and therefor increase relative pressure to the front by about 30%. The overall larger pistons will make the pedal higher and require more force.

I could just try it out but I would like to avoid bending up lines if this is going to be a bad move. Any Ideas.

Roncallo · #2 10-25-2009, 09:36 PM

OK the 96 SL600 cylinder with BAS works but the pedal seams slightly low. I expected it to be higher than the 107 cylinder as both pistons are bigger. There is a bleed port on the side of the cylinder near the BAS motor. I had no success bleeding that. Next to nothing came out of that bleeder. Does anyone know if the BAS motor needs to be turned on some way.

In any case the SL600 cylinder appears to be a better solution however I believe I have another problem. The car still pulls severally on braking and I believe is may be a rear caliper issue. What I originally thought was rear wheels locking up first due to a bias problem, apparently may be one rear wheel locking up first.

So basically I just spent $400 rebuilding front brakes and cutting brake lines for little gain. That was more than 1/2 the cost of a much needed phantom grip rear. Breakes are the one area that I didnt rebuild on this car so I guess it caught up to me.

whipplem104 · #3 10-25-2009, 10:20 PM

Hello,
The simple answer is yes there is a special bleeding process for that brake system. I would maybe consider jumping the bas and bleeding. When we did it on a factory car there was a procedure that we went through. I do not remember for sure what it was but we ran the pressure pump and activated some solenoids. If you are not using the system the brakes should operate as though it is not there, but you may still have some air in it. Another thing to consider is that your rear brakes if they are original are smaller than the sl600 and will change the bias also.
Although I had very little problem putting bigger brakes on my car. My pedal got soft but then I put stainless frt. lines on and it works beautifully, and I have a stock master and rear brakes.

Roncallo · #4 10-26-2009, 08:50 PM

Thanks for the reply whipplem104. The bleeding seems to be a non issue. I think some air may have migrated back up to the reservoir last night. either that or as I bed the brakes the pads move less. In any case the bias still seams to suck, rears still locking up prematurely but significantly better with the SL600 cyl. I'm hoping this gets better as I bed the brakes. I'm using EBC Redstuff ceramic, they say bedding can take up to 1000 miles. I need a good weekend to ring it out. I also still have a pull to the left which also has improved with time.

Roncallo · #5 10-31-2009, 07:52 AM

Whipplem104 or Anyone

Have any ideas on how to bleed just the master on this system. I found out that thing on the master is a switch and not a motor. See my other post 12V or 5V +/- etc.

I actually have the breaks working real well now. They brake straight ahead and bias is excellent now that everything is bedded in. The pedal is still slightly low. In fact I only really notice it when I go from my stock 560 to this one , but it does shrink ones sphincter until you get used to it.

So if I managed to cure bake bias, bake pull and brake dust with the $400.00 I spent, it will all be worth it. I also discovered while I was in there that the directional rotors were installed backwards. But I would like to get the pedal up to at last as high as the stock 560SL which should not be hard given the increased piston size.

http://www.peachparts.com/shopforum/tech-help/264409-bas-theory-operation-how-bleed.html#post2328615

Fulcrum525 · #6 10-31-2009, 11:24 AM

I'm happy to see that yet another problem has been solved through a little bit of engineering

Roncallo · #7 10-31-2009, 02:28 PM

Quote:

Originally Posted by Fulcrum525

I'm happy to see that yet another problem has been solved through a little bit of engineering

Not solved yet but closing. Reverse engineering requires patience.

Roncallo · #8 11-15-2009, 06:34 PM

I finally got around to making up some leads and bleeding this thing. Yes I just applied 12 v to the two pins on the valve and it bled very nicely. 12+ on the bottom pin. Pedal is nice and high bias appears to be very good.

The next step is to take advantage of the features of this valve. For the SL600 it is activated off the lateral accelerometer. Which I happen to have installed and wired. I need to see If I can get a signal to this valve without having the rest of the ESP system up and running.

Thanks for the help everyone.